Thanks for all the input - here's a summary of theories, with my
comments and further questions for all you enginologists:
* Valve float due to high revving / missed shift / "spirited"
driving - I don't think this is the case, at least not just prior to
failure - I was just taking off, and going rather slow. Engine may have
been a tad cold.
* Rockers not adjusted - I suppose, but they never made any noise
prior to this
* Stock rocker arms may not have enough clearance for high lift
cam - would this have lasted 3000 miles? How do I check this?
* Springs too big / not enough clearance - would this have lasted
3000 miles? How do I check this?
* Pressed in rocker arm studs may have pulled out and loosened the
rocker arm. How do I check this? I think mine are threaded, but not
sure.
* Mismatched rockers & heads (e.g., big guide holes and no
rail-type rockers, or guideplates with non-hardened pushrods) - I don't
think this is the case, but don't have a sense for how tight the
clearance in the guide holes should be with flat faced (no rails)
rockers. My heads have a hole where the pushrod goes in, lots of play
up and down, and around 0.050" side to side. I'm not sure what a
guideplate looks like, or what the clearance in the head-hole should be.
This is likely the origin of the old expression "I need that like a I
need a hole in the head."
Tim, in specific response to your questions:
* Is it possible that the Rocker bound on the rocker stud? - I'm
not sure what to look for, but the rocker and stud looked OK.
* Is it possible that the springs coil bound? Also not sure what
you mean by this, or what to look for.
* Is the cam solid or mechanical? Are you referring to a roller
cam? I have hydraulic lifters. This is something I've always wondered
about: All cams are solid, no? The lifters are either solid, hydraulic,
or have rollers. When people refer to "roller cams" or "hydraulic cams"
does this refer to the cam profile to accept certain types of lifters?
Sorry if I seem like I just fell off the turnip truck...
* What is the clearance between the spring coils at max lift? Is
there a spec for this? Do I just rotate engine until valve is full open,
then measure clearance between the coils?
* Were they both Intake valves? Yes
* Are there valve reliefs milled into the pistons? Not sure,
rebuild was 15 years ago
* Did you check valve to piston clearance? I didn't build the
motor. How is this done, through the intake/exhaust port?
* Do you have guideplates and if so do they show any wear? No,
just the holes in the heads.
I think if a valve was hitting a piston, it would have happened earlier,
believe me, I've done more, uh... "spirited" driving in the past.
Thanks again to all, please let me know what you think some more - I'll
be tearing into it this weekend.
Arnie
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